The present invention relates generally to digital subscriber line communications and more particularly to a method for scheduling data for communication on a digital subscriber line.
Many digital subscriber line (xDSL) systems use an asynchronous transfer mode (ATM) protocol to schedule the transmission of cells encoding voice, data and signaling information. Using an ATM transmission protocol, cells are scheduled for transmission on an xDSL link according to guaranteed data rates for different communications streams. Typically, voice and signaling cells are guaranteed bandwidth since these communications are time critical. Data cells may be scheduled into the gaps in voice communications and signaling. ATM compliant systems using permanent virtual circuits (PVCs) to transmit voice, data, and signaling adhere to strict guidelines for the scheduling of cells.
If the xDSL link does not provide sufficient bandwidth to meet the guaranteed minimum bandwidths for voice and signaling PVCs, PVCs may be disconnected, PVCs may be downgraded such that all cells are scheduled for transmission without a guaranteed bandwidth, or an administrator may manually adjust the guaranteed bandwidths. Disconnecting a PVC prevents any communications and may also interrupt current communications session. Downgrading PVCs allows an ATM compliant system to continue the transmission of cells using proper scheduling, but it also forces voice and signaling cells to compete with data cells for bandwidth. During periods of intense data communications, this may result in a serious degradation in the quality of voice communications since bursts of data may starve out voice communications.
In accordance with the present invention, a method for scheduling data for communication on a digital subscriber line is provided which substantially eliminates or reduces disadvantages and problems associated with previous systems and methods. In a particular embodiment, the present invention satisfies the need for a scheduling technique that preserves the quality of voice communications when the available bandwidth of a digital subscriber line falls below a guaranteed minimum bandwidth.
According to one embodiment of the invention, a method for scheduling cells associated with a plurality of communications channels on a digital subscriber line determines an available bandwidth of the line and determines a required bandwidth for the communications channels. The method compares the required bandwidth and the available bandwidth, and based on the comparison, selects a first mode of operation or a second mode of operation. In the first mode of operation, the method schedules the communication of the cells using an asynchronous transfer mode (ATM) communications protocol. In the second mode of operation, the method schedules the communication of the cells using a high priority queue in combination with the ATM communications protocol.
In accordance with another embodiment of the present invention, a method for establishing a priority hierarchy for a plurality of communications channels on a digital subscriber line determines that a required bandwidth for the communications channels exceeds an available bandwidth of the line and assigns a selected one of the communications channels to a high priority queue. The method schedules cells associated with the communications channels using the high priority queue in combination with an ATM communications protocol.
The invention provides a number of technical advantages. While systems that strictly comply to ATM scheduling protocols may potentially suffer severe degradation in the quality of voice communications, this method provides a modification to existing ATM protocols to ensure the quality of voice communications when the available bandwidth on an xDSL link falls below a configured level. During these low bandwidth periods, ATM protocols force voice, signaling, and data cells to compete equally for the same bandwidth. Bursty data communications may starve out time critical transmissions such as voice communications during these intense periods. When the available bandwidth of an xDSL link is insufficient to provide guaranteed bandwidth to voice communications, voice communications channels are removed from the ATM scheduling protocol and scheduled separately using priority queuing.
Other technical advantages of the present invention will be readily apparent to one skilled in the art from the following figures, descriptions, and claims.